"useless unless you actualy know your total draw of all your equipment runing. Lamps,ac,fans,filters,even timers."
The light is used as the point of measure because that is the specific energy draw the plant uses to grow. not the AC. you can grow with no AC but you cant grow with no light. capiche??
"Think about it this way if your using a 1000 and 1800 watts of ac to grow 2lbs and your buddy is using just a 1k light and getting 15zips are you really the more efficent grower"
the only way to compare would be for you to grow in his setup and then compare.
This method is not for comparing different grow operations to one another. this system is designed to compare cycles in one operation.